The invention relates to index table assemblies for machine tools and the like and more specifically to an index table assembly having an actuating mechanism for rotating an index table to a plurality of positions and quickly and accurately locating the index table at each position.
In the past, index table assemblies have been such that the associated index tables have normally been rotated in only one direction between indexed positions. Such index table assemblies require that the index table be precisely stopped in the desired indexed position; yet it is desirable that the table be rotated at a relatively high rate of speed for as long as possible to decrease the indexing time between indexed positions. At the same time the rotational velocity of the index table often is prematurely reduced in order to prevent overshoot. In addition, rapid deceleration and abrupt stops can put high stresses on the actuating mechanism of the index table assembly, which may result in improper indexing and/or in early failure of the operative parts.
With prior index table assemblies, the index table has often been supported on roller bearings or the like to relieve friction between the index table and the supporting structure to permit indexing of the table with a conventional drive structure. Such bearings are in permanent contact with the table and may not provide a steady base for such index tables at their indexed positions. Further, such bearings are subject to wear and thus require periodic checking and adjustment or replacement if the required accuracy of most index tables is to be maintained.
Also, some prior index table assemblies have not been provided with a structure for holding the table in an indexed position other than the structure required for initially positioning the index table in the indexed position. In this regard it has been known to use a shot pin assembly to hold the index tables in the desired positions. But such shot pin assemblies were not securely locked and could loosen resulting in inaccurate positioning. Maintaining such prior index tables in their indexed positions has thus been less secure than desirable. Where a separate assembly for holding prior index tables in indexed positions has been provided, it often has been internally buried in the index table structure so as not to be readily available for maintenance or inspection.